Rotary pump for liquefied gases



April 1949- r R. v. CARLSON 2, 68,171 ROTARY PUMP FOR LIQUEFIED GAS ESFiled Jan. 9, 1947 INVENTOR ROGER V. CARLSON wuved/ ATTO R N EY PatentedApr. 26, 1949 UNITEDVISTATIES PATENT OFFICE ROTARY PUMP FOR LIQUEFIEDGASES Roger V. Carlson, Kenmore, N. Y., assignor to The Linde AirProducts Company, a corporation of Ohio Application January 9, 1947,Serial No. 721,135

8 Claims. (Cl. 103-'96) This invention relates to rotary pumps forliquefied gases having normal boiling points substantially below.233 K.,such as liquid nitrogen, and particularly to inboard bearings for suchpumps.

The pumping of liquefied gases having low boiling points involvesunusual problems due to the great volatility of the liquid and itsextremely low temperature. The volatility of the liquid, which isincreased by natural heat flow toward the liquid from the surroundings,makes pumping of such a liquid quite difficult as generation of heat bythe operation of the pump may cause gas binding and failure ofoperation. The low temperature also makes it impossible to employordinary lubricants and therefore bearings of the customary type cannotbe used.

2 between races out of contact with each other, which means is operablein contact with the liquefied gas without requiring liquid or semi-solidform of plastic ball retainer employed in the bear- To obtain higherdelivery pressures when pumping a liquefied gas by rotary pumps it isfound necessary to employ two or more stages and when several stages areprovided in a single casing with a single drive shaft the diflicultiesof accommodating the contraction of the parts have previously resultedin the employment of complicated constructions. Multiple stagingintroduties the problem of interstage sealing, which is necessarybecause the increased energy of the liquid in the higher pressure stagecauses vaporization if it leaks toward a lower pressure stage. Suchinterstage sealing must be accomplished without incurring excessivefriction and also be unaffected by expansion and contraction of theparts. It has also been proposed to use bearings made of bonded carbonor graphite in pumps for low temperature liquefied gas, particularlyliquid oxygen. Such material is self-lubricating and is not affected bythe low temperature. It does have the disadvantage, however, that ittendsto wear rapidly under the high radial bearing loads which occur inturbine type rotary pumps operating at high discharge pressures. Thussolutions that may suggest themselves for many of the dimculties areconflicting in that they may enhance others.

The principal objects of the present invention are therefore to providea pump for liquid nitrogen or liquid oxygen embodying an improvedcombination of features and association of parts that successfullyovercomes the difficulties set forth above; to provide in a two-stagerotary pump for liquefied gas an improved combined bearing andinterstage seal; and to provide in a liquefied gas rotary pump a meansfor keeping the rolling elements, such as balls, of an inboard bearingof the type having rolling elements ing according to the invention.

Referring now to the drawing, the pump illustrated is of the two-stagetype and has a main frame or casing I'll containing first and secondstage annular pumping channels II and I2 with a partition l3 betweenthem. Operating in the pumping channels it and I2 are rotary impellersl4 and I5 respectively provided with suitable blades It at theirperipheral portions for propelling the fluid through the pumpingchannels. Each pumping channel is provided with a suitable inlet andoutlet passage, which passages do not appear in the section shown. Theoutlet of the first stage channel II is connected to the inlet of thesecond stage channel l2. The arrangement of the pumping channels andtheir inlet'and outlet passages is similar to that shown and describedin U. S. Patent No. 2,340,787, but is not illustrated herein since itforms no part of the present invention. One side of the casing I0 isclosed by a cover II which is shaped internally to form part 01 thepumping channel l2 and to provide close clearance between it and oneside of the impeller l5 and has a cup-like central depression i8 forenclosing the hub is of the impeller IS. The other side of the casing I0is provided with a closure 20 similar to the cover I! but having anannular central portion 2| providinga closure for the hub portion 22 ofthe impeller M. A tubular extension 23 for enclosing an extended driveshaft 24 is secured gas-tightly to the central portion 2|.

The drive shaft 24 extends axially into the casing l0 and the impellersl4 and I! are rigidly secured thereon. To this end the drive shaft 24has an integral collar 25 adjacent the inner side of the impeller l4,the hub portion 22 of which extends to the. left and is. internallythreaded to engage threads 26 formed on the shaft 24. The

3 impeller I4 is thus threaded on the shaft 2| to abut tightly againstthe collar 25. To the right of the collar 25 the shaft has a cylindricalportion 21 adapted to carry the inner race 28 of a-bearing assemblyindicated generally at29. The bearing 29 is of the type having rollingelements between annular races, preferably a ball bearing. The innerside of the impeller I is provided with an annular portion 30 thatclamps the race 29 against the collar 25. The rightwardly extending hubportion l9 of theimpeller l5 is internally threaded to engage threads 3|formed on the inner end of the shaft24. If desired, the end of the shaftmay be formed with flat areas as at 3| to provide a means for grippingit with a wrench so that the impeller l5 maybe secured tightly.

The ball bearing 29 is preferably of the type I race 28 and an outerrace 33. the balls being spaced from each other by an annular retainer34. The retainer 34 may be a composite ring providing pockets for theballs and is preferably constructed of a material that in effect isselflubricating under the conditions of operation, that is, when subjectto the presence'of the liquefied gas being pumped. Self-lubricating asused herein means that the coeilicient of friction between the materialand a smooth metal ball is very small and the rate of wear is low. Whenpumping .liquid nitrogen it will be preferable to form the retainer 34of a plastic material such as a thermosetting resin bonded structurehaving a low coeflicient of friction under low temperature conditions asmore fully described hereinafter.

The outer race 33 is rigidly secured in the partition l3 byretainingrings 35 and36. To this end the partition l3 has an openingtherethrough with a shoulder 31 and an enlarged threaded counterbore 38.The rim of the ring 35 has threads engaging the threads 38 and abutstightly against the shoulder 31. The ring 35 has a bore 39 into whichthe outer race 33 is fitted so as to abut against the bottom of the bore39 formed by an annular flange or shroud portion 40 of the ring 35. Theshroud portion 40 extends radially inwardly for a distance suflicient tocover the space between the inner and outer races. The outer race isclamped in place by the ring 36 which has external threads engagingthose of the counterbore 38 and has at its inner rim a shroud ll whichcovers the space between races 28 and 33. The shouds 40 and 4| form alabyrinth type of interstage fluid seal to impede flow of liquid fromthe high pressure stage through the ball bearing and into the lowpressure stage. The retaining ring 34 is also preferably constructed toprovide small clearances with the rims of the inner and outer races 28and 33 in order to cooperate in creating a labyrinth fluid seal.

The shaft 24 passes through'a stuffing box at the outer end of thehousing 23, which stufiing box maybe of the customary type or, forexample, as shown in U. S. Patent No. 2,296,640. A supporting bearing isalso provided at the outer end of the shaft 24 which may be of anycustomary type provided that it allows for axial 4 expansion andcontraction movement of the outer end of the shaft.

From the above description it will be seen that a great simplificationof construction has been effected in a rotary multi-stage pump for lowtemperature liquefied gases. Previously there were provided axiallyadjustable connections between the drive shaft and the impellers, thrustbearing means for centering each impeller in itspumping channel, meanssuch as balance cylinders for counteracting the resultant radial forceof the liquid pressure acting on the high pressure stage impeller, andmeans for reducing the axial pressures acting on the impeller hub.According to the invention, such complications are avoided by utilizinga rolling element type of bearing positioned in the partition betweenthe impellers, the bearing being constructed to withseparator is foundto give good resultsin resisting the combined radial and axial forcesbecause the rotating speeds of the pumps are in excess of 1,500 R. P. M.For heavier duty a double-row ball bearing with two separate ballretainers-may be substituted for the single-row type. v p

The invention relies in part upon the discovery that metal bearings ofthe rolling element type are successfully operable without customarylubricants when subject to low temperature liquefled gases. It has beenuniversal practice to run ball bearings in an oily or grease lubricanteven though there is very little if any sliding friction. The lubricantpreserves the fine finished surfaces of the balls and races and removesheat due to the metal resilience at the rolling contact points. In thepump according to the inventionno oily lubricant can be used andalthough the liquefied gas such as liquid nitrogen does not appear toprovide any lubricating qualities for sliding friction, it is inert withrespect to the metal of the bearing and it effectively removes therolling contact heat. For satisfactory operating life it is alsonecessary that the rolling elements shall not contact with each other sothat there is no sliding friction between adjacent elements. Thus tokeep the balls spaced from each other a retainer 34 is employed. Thismay be a ring-shaped member provided with pockets or holes for the ballsand be made of two parts for easy assembly of the bearing.

In bearings of this type operating under a radial load that portion ofthe bearing carrying the load is known as the loaded zone. The rollingelements have to be urged into the loaded zone and the force urging therolling elements into the loaded zone is exerted by the retainer. Inaddition the rolling elements entering and leaving the loaded zonetravel at different speeds. As a result some friction is producedbetween the rolling elements and the retainer.

According to the invention it has been found that the retainer shouldpreferably be made of a material that is self-lubricating under theconditions, i. e., one that has a very low coefiicient of frictionagainst polished metal when in the presence of the low temperatureliquefied gas. A material found particularly effective is a resinbondedstructure that has adequate strength and elasticity at very lowtemperature and is inert with respect to the liquefied gas being pumped.A suitable material for the retainer is a laminated structure made offibres bonded with a heathardened phenolic resin. A number of theplasties are suitable, provided they are free of objectionableplasticizing agents. In addition to the phenol-formaldehyde resins theremay be used the polyester type such as the glycol esters with addedcross-linking agents, melamine and urea type resins provided they aresuitably modified to increase their toughness, and vinyl polymers alsosuitably toughened. Where the resins are not readily machinable, theball retainers can be made by a casting or moulding process. In any ofthese structures various fabric and fibrous materials may be employed asthe filler and the structure may include self-lubricating agent such asgraphite. When liquid nitrogen is to be pumped, any of the plasticmaterials may be employed but when the liquefied gas is not inert, theplastic must be selected for its resistance to the action of such gas,for example when liquid oxygen is pumped it is preferable 'to select aplastic which is very resistant to combustion in oxygen. An effectiveretainer for a liquid nitrogen or liquid oxygen pump ball bearing ismade from 'a laminated stock consisting of layers of fabric bonded witha heat-hardened phenolic resin. For example a suitable stock is made byimpregnating duck fabric with a heat-reactive cresol-formaldehyde resinin alcohol solution in amount to leave a resin content of about 50% ondrying to a low volatile content of about 2%. Layers of such impregnatedfabric are stacked and pressed at about 1000 pounds pressure at 300 F.for about an hour, and the laminated stock so formed is after-baked to aRockwell hardness of about 105 to 110 on the M scale. The hardness testis that referred to in procedure D785-44T of the American Society forTesting Materials.

The metal of the bearing should be chosen according to the character ofthe liquefied gas being pumped. With non-oxidizing gases such as liquidnitrogen the bearing balls and races may be made of the customary carbonor low alloy tool steels provided that care is taken to prevent rustingbefore the pump is put into service. In a pump for liquid oxygen,rusting during idle periods may be difficult to prevent and it will bepreferable to use bearings made-of the hard stainless metals such asstainless steels. Certain hard surface corrosion-resistant surfacetreatments may also be used. I 1

For efficient operation, excessive leakage 'from the high pressure stagetoward the low pressure stage should be prevented. To this end thebearing is constructed to prevent 'or limit such leakage. With a ballbearing, adequate sealing may be accomplished by the shroud flanges 40and 4| that cover the space between the races 28 and 33 and that arearranged to have a very close running clearance with the sides of theinner race 20. The clearance between the side of the impeller l5 and thering 36 is also kept small so that in effect a labyrinth type of seal isprovided. Such sealing arrangement is found to be adequate as a smallamount of leakage can be tolerated without a measurable effect on thepump ing. Such small amount of leakage is advantageous to bringliquefied gas into contact with the rolling elements which are therebyadequately cooled by a clean liquid.

Alternatively suificient sealing may be provided by the retainer 34which may be constructed to have a radial width that substantially fillsthe lateral annular spaces between the races 28 and 33. The runningclearance between the retainer and the two races can be made quite smallbecause the retainer rotates at one-half the .material isself-lubricating underthe conditions.

By constructing the retainer with close clearances, suflicientinterstage sealing may be obtained so that the use of the shroud flanges40 and 4! may be eliminated to further simplify the pump structure.

Although a preferred embodiment has been described in detail, it iscontemplated that changes may be made and certain features of theinvention may be used without others without depart ing from the spiritand scope of the invention. For example, inboard ball bearings withplastic ball retainers may be used in single stage pumps and inmulti-stage pumps on the sides of the impellers other thanintermediately between them.

What is claimed is:

1. A multi-stage rotary pump having a casing, at least two rotaryimpellers therein, an annular pumpin channel for the peripheral portionof each of said impellers, and an axially extending drive shaft for saidimpellers, said casing having a partition between the pumping channels,said impellers being secured to said shaft on opposite sides of saidpartition, and a main inboard bearing for said shaft positioned betweenthe impellers and mounted in said partition, said bearing having rollingelements between inner and outer races and including inter-stage fluidsealing means, and a retainer for keepin the rollin elements separated,said retainer being made of a self-lubricating material.

2. A multi-stage rotary pump according to claim 1 in which said bearingis a ball bearing having its inner race secured to the shaft and theouter race supported in said partition and said retainer is made of aplastic composition.

3. A multi-stage rotary pump according to claim 1 in which said bearingis a ball bearing containing no lubricant and said retainin means is alaminated structure made of fibres bonded with a heat-hardened phenolicresin.

4. In a rotary pump for liquefied gases having boiling points below 133K., such as liquid nitrogen, said pump having a casing, at least onerotary impeller in the casing, and a drive shaft for the impeller, amain inboard bearing for said shaft in said casing exposed to theliquefied gas being pumped, said bearing havin rolling elements betweeninner and outer races and having a retaining means to keep the rollingelements out of contact with each other, said retaining means'being'madeof a solid self-lubricating material.

5. A rotary pump for liquefied gases according to claim 4 in which saidretaining means is made of a laminated fibrous plastic-bondedcomposition.

6. A rotary pump for liquefied gases according to claim 4in which saidbearin is an unlubricated ball bearing and said retaining meanscomprises a laminated structure made of fibres bonded with aheat-hardened phenolic resin.

7. A m'ulti-stage rotary pump having a casing, at least two rotaryimpellers therein, an annular pumping channel for the peripheral portionof each of said impellers, and an axially extending drive shaft for saidimpellers, said casing having a partition between the pumping channels,said impellers being secured to said shaft on opposite sides of saidpartition, and .a bearin for said shaft positioned between theimpellers, said bearing being a ball bearing with its inner race securedto the shaft and its outer race mounted in said partition, and aretainer made of a plastic 7 composition constructed for keeping thebearing balls separated, said retainer being thick enough tosubstantially close the space between the races and provide a fluid sealfor impeding the flow of liquid through the bearing from the hi herNumber Name Date 928,327 Prindle July 20, 1909' 2,035,417 AllendorfiMar. 24, 1936 2,281,971 Goddard May '5, 1942 made of a solidself-lubricating material and be-' ing constructed to have a radialthickness such that the space between the races is substantially closedby the retainer to impede movement of liquefied gas through the bearing.

. ROGER V. CARLSON.

REFERENCES CITED The following references are of record in the 10 fileof this patent:

UNITED STATES PATENTS

